In general, a midplane is a circuit board which connects to other circuit boards on each side. Midplanes are often used in data storage systems where one side of the chassis accepts processing cards (e.g., storage processors) and the other side of the chassis accepts other types of cards such as I/O cards and service modules. Typically, power supplies connect to the midplane, and the midplane distributes power to the other circuit boards. Midplanes are suitable for use in other types of systems as well such as networking systems.
One conventional midplane has a portion that connects to a connector on each side. In particular, on a first side of this midplane portion, there is a first connector footprint which connects to a first midplane connector. On the opposite side of this midplane portion, there is a second connector footprint which perfectly overlaps the first connector footprint and which connects to a second midplane connector having the same design as the first midplane connector.
The midplane portion includes a group of plated through holes (PTHs) which are carefully arranged so that compression fit pins of the first connector insert into certain PTHs of the group through the first side of the midplane. Similarly, compression fit pins of the second connector insert into certain PTHs of the group through the second side. The midplane and the PTHs are deep enough so some of the PTHs, which are called “shared vias”, receive pins through both ends without the pins interfering with each other. Such shared vias allow the two midplane connectors to connect with each other through the midplane without copper traces. The remaining PTHs of the group, which receive pins from only one connector, are connected to ground to improve signal integrity of the signals passing through the shared vias. Connectors which are similar to the above-described connectors are the I-Trac™ connectors offered by Molex Incorporated of Lisle, Ill.